Promise() as text in Label

shokarta

hello,

considering:

Repeater {
  count: 999

  function calculateDate(input) {
      var result = something_this_takes_too_much_of_the_time * input;
  }

  Label {
    text: return (new Promise(resolve =>   calculateDate(somevalue)   )).then(text => text)
  }
}

as far as await function does not work in QML, Promise is good alternative not to block GUI when calculateDate() is calculating and text should be slowly populating one by one

this is at least my udnerstanding of Promise(), never used it before

unfortunatelly, this does not work, it gives me error:

Unable to assign QJSValue to QString

when I try:

return (new Promise(resolve =>   calculateDate()   )).then(text => text.toString())

return (new Promise(resolve =>   calculateDate().toString()   )).then(text => text)

but:

return (new Promise(resolve =>   calculateDate()   )).then(text => text).toString()

only display text as "[object Promise]"

so how do I achive what I am looking for?

GrecKo

You don't. That's not how promises work. then doesn't return a value, it takes a function that will be eventually called and returns the promise itself (the QJSValue or [object Promise] you see).
Also you need to call resolve when writing a promise to indicate it is finished : (resolve => resolve(calculateDate)));

More info here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises

What you could try doing is declaring a new Binding and use the fact that it can change a property, something like the following:

// PromiseBinding
import QtQml

Binding {
     property var promise
     onPromiseChanged: promise.then(v => value = v)
}

Usage would be like this:

Label {
    PromiseBinding on text {
        promise: new Promise (resolve => resolve(calculateDate().toString()))
   }
}

Disclaimer: I haven't tried that.